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Volume 10 Issue 2, February 2018

Although enzymes that catalyse transformations in the biosynthesis of natural products often demonstrate remarkable activity and selectivity, there are typically challenges — usually relating to substrate scope and stability — that must be overcome before they can be used effectively in the laboratory by synthetic chemists. Now, a team led by Alison Narayan has shown how three related enzymes that are known to catalyse the oxidative dearomatization of phenols and resorcinols can be used to make ortho-quinol products (an example of which is depicted on the cover) with impressive site- and stereoselectivity. The method is robust enough to be scaled-up to gram-scale reactions and its use in multi-enzyme and chemoenzymatic cascades has also been demonstrated.Article p119IMAGE: STEPHANIE KING, THE UNIVERSITY OF MICHIGAN LIFE SCIENCES INSTITUTECOVER DESIGN: TULSI VORALIA

News and Views

Using infrared light to control the outcome of a chemical reaction is problematic in solution because of numerous interactions and non-specific sample heating. Now, condensed-phase results showing the vibrational enhancement of an otherwise thermally driven reaction may reinvigorate discussion of the practical applications of vibrational control.

Mass spectrometry is a powerful technique for analysing proteins, yet linking higher-order protein structure to amino acid sequence and post-translational modifications is far from simple. Now, a native top-down method has been developed that can provide information on higher-order protein structure and different proteoforms at the same time.

Articles

Within natural product biosynthetic pathways, nature has evolved highly selective catalysts capable of complexity-generating reactions. Leveraging these tools, a suite of catalysts with complementary site- and stereoselectivity have been applied to the oxidative dearomatization of phenolic compounds, enabling one-pot transformations of phenols into various natural products.

A practical realization of selective IR-driven reaction-rate control has been hampered by competing processes leading to sample heating. Now, the acceleration of a bimolecular ground-state reaction in solution using the IR excitation of a vibration connected to the reaction coordinate is demonstrated. The behaviour is monitored and understood using a combination of femtosecond IR-pump IR-probe spectroscopy and theoretical calculations.

A centimetre-long string formed by the hierarchical self-assembly of a photoresponsive amphiphilic molecular motor — composed of 95 wt% of water — undergoes muscle-like contraction. Under irradiation, rotary motion at the molecular level is amplified through non-covalent interactions to sustain a fast macroscopic mechanical motion of large amplitude.

An integrated native mass spectrometry and top-down proteomics method using Fourier transform ion cyclotron resonance has been developed for the characterization of macromolecular protein complexes. This approach directly yields primary to quaternary structural information in a single native top-down experiment.

Water oxidation is key to the production of chemical fuels from electricity. Now, guided by theory, NiCoFeP oxyhydroxide catalysts have been developed that require an overpotential lower than that required by IrO2. In situ soft X-ray absorption studies of neutral-pH NiCoFeP catalysts indicate formation of Ni4+, which is favourable for water oxidation.

Primer exchange reaction (PER) cascades have now been used to grow nascent single-stranded DNA with user-specified sequences following prescribed reaction pathways. PER synthesis occurs in a programmable, autonomous, in situ and environmentally responsive fashion, providing a platform for engineering molecular circuits and devices with a wide range of sensing, monitoring, recording, signal processing and actuation capabilities.

Tau aggregation is associated with Alzheimer's disease and dozens of related dementias. Now atomic structures of the aggregation-prone segment VQIINK in repeat 2 of tau have been reported. Inhibitors designed using these structures block seeding by full-length tau better than inhibitors that target the VQIVYK aggregation segment in repeat 3.

Spectroscopists and theorists are closing in on an understanding of the origin of oscillatory features in the spectral response of light-harvesting complexes to femtosecond pulsed excitation. Now, the photosynthetic Fenna–Matthews–Olson complex is probed by femtosecond pump–probe spectroscopy and compared with a series of genetically modified mutants with distinct excitonic interactions, allowing electronic and vibrational contributions to coherence to be distinguished.

DNA–polymer conjugates are attractive materials that combine the programmability of nucleic acid assembly with polymer functionality. Now, through a DNA cube template, monodisperse polymer particles have been imprinted with several DNA strands in pre-designed orientations— each independently set and addressable. The resulting hybrid particles can further assemble into well-defined, non-centrosymmetric structures.

Catalytic transformations that incorporate carbonyl functional groups in arene C–H bonds have remained limited, despite being attractive synthetic steps. Now, the intermolecular carbonylative coupling of a broad range of simple arenes into ketones has been developed. The reaction occurs through the palladium-catalysed generation of high-energy aroyl triflate electrophiles.

Oxidation chemistry is critical to introducing molecular complexity during chemical synthesis. Development of sustainable oxidation chemistry demands strategies to harness O2 as a terminal oxidant. Access to hypervalent iodine compounds — a class of broadly useful chemical oxidants — from O2 increases the scope of aerobic oxidation chemistry that can be achieved.

Selectively targeting native amino acids for late-stage protein modification is a significant challenge, but now it has been shown that photoredox catalysis can be used to specifically target protein C-termini toward decarboxylative-alkylation with Michael acceptors. This technology harnesses innate differences in side-chain oxidation potentials to select between the various functional groups typical among proteins in order to form a single modified product.

Phosphorylation of (pre)biological molecules in water has been a long-sought goal in prebiotic chemistry. Now, it has been demonstrated that diamidophosphate phosphorylates nucleosides, amino acids and glycerol/fatty acids in aqueous medium, while simultaneously leading to higher-order structures such as oligonucleotides, peptides and liposomes in the same reaction mixture.

The direct arylation of C–H bonds is an attractive synthetic step, but the reductive elimination of an organometallic catalyst carrying the desired C–H and aryl functionalities has remained challenging. Now, this step has been achieved by first oxidizing the iridium centre of the catalyst, which facilitates the arylation of arene C–H bonds of a range of substrates.

The ability to merge the photophysical properties of semiconductor quantum dots with those of well-understood and inexpensive molecular chromophores is important for the development of various emerging photonic and optoelectronic technologies. Now, 1-pyrenecarboxylic acid-functionalized CdSe quantum dots have been shown to undergo thermally activated delayed photoluminescence and display tunable photophysical properties.

The anthraquinone and enediyne halves of the antitumor antibiotic dynemicin A were previously thought to be assembled by two separate polyketide synthases (PKS). Now, a single polyketide synthase has been proposed to be responsible for their production, and a working model for their biosynthesis from a common octaketide intermediate has been suggested.

Short-lived intermediates in solution may react before undergoing thermal equilibration. This phenomenon is used here to achieve the ‘energy labelling’ of an alkoxy radical. The intermediate's excess energy varies broadly depending on how it is formed and can be determined from the observed reaction selectivity.

Hiroaki Kurouchi

& Daniel A. Singleton

In Your Element

Shawn C. Burdette and Brett F. Thornton explore how germanium developed from a missing element in Mendeleev's periodic table to an enabler for the information age, while retaining a nomenclature oddity.